1. The problem statement, all variables and given/known data I am not yet at the chapter of equations of equilibrium, plus it says the couple moment is not 0, so I assume it just about the loadings and not including the reactive forces and reactive moment. 2. Relevant equations F= 1/2*b*h M= 1/2*b*h*d 3. The attempt at a solution So if I call the top one F1 and the bottom loading F2 I got: F1+F2=0= -4*b*1/2+2.5*(b+a)*1/2 solving this i got a=0.6b Moment around the of the bar (not A, but opposite side) due to the loadings is (counter clockwise positive): M= -F1*center of triangle + F2*center of triangle Because you can replace the loading with force F1 and force F2 and its line of action is through the center of the triangle area (1/3* base) M= -8= -4*b*1/2*1/3b+2.5*(b+a)*1/2*1/3*(b+a) So what am I doing wrong? Because M can never be negative with me, plus the answer should be b= 5.625 and a= 1.539. But this to me makes no sense, because then F1+F2 is not 0. And if I should take the reactive forces into account at A then you can never have still a moment, because then it is not static anymore.